1. Field of the Invention
The present invention relates to a nonvolatile RAM, and more particularly, to a resistance RAM.
2. Description of the Related Art
Currently, in the case of a flash memory that is commercialized with a nonvolatile memory, an electric charge is stored or removed in an electric charge storage layer, such that a change in threshold voltage is used. The electric charge storage layer may be a floating gate that is a polysilicon layer or an electric charge trap layer that is a silicon nitride layer. Recently, a novel nonvolatile RAM that has low power consumption and high degree of integration as compared to the flash RAM has been studied. As examples of the novel nonvolatile RAMs, there are a phase change RAM, a magnetic RAM and a resistance RAM.
The resistance RAM may have a structure in which a solid electrolyte layer is inserted between metal electrodes. This element may generate or remove a conductive channel by an electrochemical reaction in the solid electrolyte layer, and two resistance states, that is, a low resistance state and a high resistance state, can be shown in accordance with the presence of the conductive channel. However, it is very difficult to control the formation position and the formation amount of the conductive channel. Accordingly, when the element is switched repeatedly, since resistor distribution of each of the low resistance state and the high resistance state is very large, a nonuniform resistance switching characteristic may be shown, and because of the large resistor distribution of each of the two resistance states, it is difficult to discriminate the two resistance states.